Biological ore processing for the isolation of heavy metals

An assay for identifying a bacterium capable of binding elemental gold and/or silver, comprising the following steps:

• (i) cultivating a test bacterium in a suitable first culture medium;
• (ii) immersing a tip portion of at least one pin of a test tool into the first culture medium for a period of time that is sufficient for allowing specific adherence of the test bacterium that can bind gold and/or silver, said tip portion being coated by elemental gold and/or silver;
• (iii) removing said tip portion from said first culture medium and rinsing or washing the tip portion for removing not-specifically bound bacterial cells from the tip portion;
• (iv) contacting a second culture medium with the tip portion coated by elemental gold and/or silver of said test tool removed in the previous step for inoculating the second culture medium with any test bacterial cells adhering to the tip portion of the at least one pin of the test tool;
• and
• (v) identifying the test bacterium as being capable of binding elemental gold and/or silver from growth of the test bacterium in said second culture medium.